The objective of this project is to develop the technique of NMR-assisted cryosurgery and to demonstrate its effectiveness for creating a definable zone of necrosis in three typical organ tissues. Cryosurgery is a treatment in which cancerous tumors are frozen and then left in situ to be absorbed. It can be highly effective in treating solid tumors and can offer hope when other treatments are ineffective. However, the application of cryosurgery to deep body tissues is prevented by the inability to observe the transient, irregular shape of the frozen region during treatment and by an inability to know the exact relation between the frozen region and the destroyed tissue. The eventual goal of this project is to provide the cryosurgeon with the ability to plan optimal freezing protocols and then observe and modify the freezing process during the cryosurgical treatment of cancerous tumors. The project will develop fast NMR imaging techniques for monitoring the extent of freezing in real time and in 3-dimensions. Gelatin phantoms, rabbits and dogs will serve as experimental models. Brain, liver and prostate tissues will be studied because cryosurgery could be used effectively in these three tissues. Special cryosurgical probes will be developed to satisfy the requirement that no metallic materials be used inside and NMR magnet bore. In order to establish the effectiveness of the NMR imaging to predict the extent of tissue destruction, post- cryosurgical changes in tissue viability will be evaluated over a period of hours to days after freezing using standard histologic and electron microscopic analytic techniques. The results of these analyses will be correlated with 1H NMR images obtained during and after freezing. A mathematical model of the temperature distribution in both the frozen and unfrozen regions will be developed and solved in 3-dimensions using the finite enthalpy technique. The model will be implemented on a computer for the purpose of pre-treatment planning. A model that computes temperature distribution using the boundary at the frozen region detected by NMR imaging will be developed for monitoring and controlling cryosurgical procedures. Successful completion of this project will establish NMR imaging as an effective means of monitoring the cryosurgical freezing process and provide a basis for the clinical application of cryosurgery to solid tumors located in the brain or internal organs.